Medical devices such as pacers and defibrillators typically include at least one lead assembly. In a defibrillator, for example, a lead assembly typically includes at least one defibrillation electrode, such as a defibrillation coil. Some lead assemblies include a cover that extends over at least a portion of the outer surface of the lead assembly. A cover may extend over a defibrillation coil, for example. Covers are used, for example, to prevent tissue ingrowth. Some covers are formed from polytetrafluoroethylene (PTFE). Improved coverings for lead assemblies are needed.